1. Statement of the Technical Field
The invention concerns ad-hoc radio networks, and more particularly methods to facilitate late entry of nodes into ad hoc radio networks that use frequency hopping sequences that are non-deterministic.
2. Description of the Related Art
Frequency agile communication systems can hop over a sequence of frequencies to avoid detection and/or interference. When such frequency hopping types of communications systems are used to form an ad-hoc network, they must include some way for nodes to enter into the network after frequency hopping has already begun. To this end, frequency hopping networks often use a pre-determined frequency hopping pattern. In such systems, a late entrant into the network can scan one or more known hopping frequencies until it detects a network communication on one of those frequencies. Once such communication is detected, the late entrant to the network can easily achieve hop synchronization with the remainder of the network, since the hopping sequence and timing are known.
Cognitive radio systems comprise radio transceivers that automatically change their transmission or reception parameters in response to a spectral environment. The active control over the parameters of transmission and reception generally relies upon certain cognitive radio activities, such as spectrum monitoring and dynamic selection of transmission frequency among network nodes. This process of dynamic frequency modification is sometimes referred to as dynamic spectrum access or DSA. In such a system, the radio transceivers automatically choose the frequency on which to communicate with each other. The frequency used to communicate is usually selected in such a way as to minimize interference with other users of the same spectrum. For example, the frequency can be selected to avoid interference with a class of wireless spectrum user which has been designated as a primary user of such spectrum.